Abstract: To promote regional economic development, Yugan County has capitalized on the abundant resources of Poyang Lake—including its wetlands, migratory birds, and traditional fishing–farming culture—leading to the establishment of an integrated agricultural rural complex known as the Poyang Lake Tianyuan Complex. This study collected 6,025 surface soil samples within this complex, and employed analytical techniques including Atomic Fluorescence Spectrometry (AFS), Inductively Coupled Plasma Mass Spectrometry/Optical Emission Spectrometry (ICP-MS/OES) and X-Ray Fluorescence Spectrometry (XRF) to measure 14 soil indicators, such as Se, Cd, N, P, and K, so as to conduct a comprehensive evaluation of soil nutrients, environmental quality, and selenium enrichment. Principal Component Analysis (PCA) and Positive Matrix Factorization (PMF) were used for source apportionment of elements including Se and Cd. The results indicate that:①The soils in the Poyang Lake Tianyuan Complex are rich in nutrients and demonstrate favorable environmental quality. Soils categorized as suitable for safe utilization are predominantly limited by cadmium (Cd) risk, which accounts for 30.32% of the area. Abundant selenium-rich soil resources are present, with a contiguous pollution-free Se-enriched area of 96.89 km².②Source analysis revealed that soil Se is mainly derived from natural sources, specifically secondary enrichment through weathering of red soil parent material, contributing 45.14%. The risk element Cd primarily originates from fluvial transport and sedimentation, with a contribution rate up to 73.51%. ③The extensive area of pollution-free Se-rich land is well-suited for developing selenium-functional agriculture. It is recommended to enhance monitoring and management of wastewater and waste residues from upstream mining activities to curb pollutant dispersion, and to adopt safe agricultural practices on contaminated farmland for the sustainable development.